Recent industrial development has created a demand for high-precision, high-speed measuring techniques. To respond to the demand, it is essential to develop optical measurement techniques with various features, such as high sensitivity and parallel processing.
The simplest method for observing fast phenomena, such as the motion or slight shape change of an object, is to directly photograph the object with a high-speed camera. To obtain object information, complex amplitude information (i.e., luminance information (intensity information) as well as phase information) is required. However, the method using a high-speed camera can only record the intensity information of an object, and cannot be applied to a transparent object.
To solve this problem, Patent Literature 1 and Non-Patent Literature 1 disclose optical measurement techniques based on interferometric techniques. A variety of interferometric techniques have been proposed, and FIG. 29 shows an optical system using a holography apparatus as an example of interferometric techniques.
In the holography apparatus 50 shown in FIG. 29, a beam splitter 52 separates a laser beam emitted from a laser light source 51 into light to illuminate an object (object light) and reference light. The object light illuminates a measurement object 100 through an objective lens 53a, lens 54a, and mirror 55a, and light that has been reflected from the measurement object 100 enters a camera 57 through a beam splitter 56. The reference light, on the other hand, enters the camera 57 through a path where the measurement object 100 is absent, more specifically through a mirror 55b, objective lens 53b, lens 54b, mirror 55c, and beam splitter 56. This enables the camera 57 to record the interference pattern (the interference fringe pattern) of the reference light and the object light, and a computer performs a predetermined computation on the basis of the interference pattern to thereby determine the complex amplitude information (intensity information and phase information) of the measurement object 100.
Interferometric techniques, however, employ light interference and thus have the following drawbacks:                the optical system is complex because of the use of many optical elements and the requirement for high installation precision;        a large optical system is required;        a coherent light source, such as a laser light source, is required; and        the techniques are susceptible to recording environments (e.g., vibration and temperature change).        
Non-Patent Literature 2 discloses a technique for obtaining complex amplitude information on the basis of the intensity information obtained by a multiple-shot recording without using light interference. FIG. 30 shows a measurement apparatus for use in such a technique.
In the measurement apparatus 60 shown in FIG. 30, the light emitted from a light source 61 illuminates the measurement object 100 through an objective lens 62, lens 63, and mirror 64, and the light that has been reflected from the measurement object 100 enters a camera 65. The camera 65 is provided on a fine movement stage 70, which moves along the propagation direction of the reflected light. Recording the measurement object 100 with a multiple-shot exposure using the camera 65, while moving the fine movement stage 70, captures multiple sets of intensity information recorded at different optical distances (optical path length) from the measurement object 100. Moreover, the phase information of the measurement object 100 is calculated from the change in intensity information using the transport of intensity equation (TIE). This makes it possible to determine the complex amplitude information of the measurement object 100.
The measurement apparatus 60 is more advantageous than the holography apparatus 50 shown in FIG. 29 in the following respects:                the optical system is simple;        the measurement apparatus 60 is not susceptible to recording environments (e.g., vibration) because light interference is not used; and        a self-illuminating object (e.g., a fluorescent object) can be measured because a coherent light source is unnecessary.Such a measurement technique is used in the field of electronic microscopes, for example. An electronic microscope using such a technique measures the intensity of electron waves in a plurality of observed planes to determine the phase so as to meet the law of electron wave propagation.        